1. Field of the Invention
This invention relates to side fire laser fiberoptic catheter apparatus, and more particularly, to side fire laser fiberoptic catheter apparatus in which elements are fused together and in which laser output is controlled by a lensed flat or a configured lens on the catheter cap.
2. Description of the Prior Art
Side fire laser catheter elements using fiberoptics are in contemporary usage in disectomy, laparoscopy, arthroscopy, benign prostate hyperplasia, angioplasty, and other related surgical procedures.
The side fire laser catheter elements include a fiberoptic element disposed within a cap. The fiberoptic element has a tip cut and highly polished at a slant angle and disposed against or adjacent to a mating secondary reflector within the cap, separated only by a small air gap. When the laser is fired, the laser output beam is reflected primarily by total internal reflection due to the difference in refractive indicies of the fiber and the air in the gap, and the angle of the cut and polished fiber. Any radiation which escapes this reflection, axially, is reflected from a secondary reflector outwardly through the side of the catheter. Since the fiber and catheter cap are cylindrical, there are cylindrical distortions in the output of the fiber. Moreover, the tip of the fiberoptic typically includes rough edges and chips and scratches on the facet which contribute to the scattering of the laser output.
In the process of fabricating the cap, silica vapor is formed, and the vapor is deposited on the inside wall of the cap, causing adsorption and reflection of some portion of laser energy. The apparatus of the prior art is difficult to manufacture, and there is typically about a 60 percent rejection rate in the manufacturing process. Moreover, in the 40 percent of the side fire laser fiberoptic catheter apparatus that is not rejected, there is typically a substantial lack of control in the output of the laser due to the problems referred to above. This is undesirable because backscattered radiation & axial transmission can cause damage to healthy tissues.
In addition, the substantial portion of scattered energy, typically about 15%, contributes to heating of the assembly during operation. This heating may result in adhesion of tissue to the cap. Carbonization (burning) of the tissue results in further energy absorption, more heating, tissue adhesion, burning, and, ultimately, failure of the cap due to pitting in the silica.
The apparatus of the present invention overcomes the problems of the prior art, as discussed above, including the rejection rate, by sleeving the fiberoptic element with a fused silica cylinder prior to forming the chisel tip or facet and by fusing the fiberoptic element to the cap to form a single element, and by providing a lens or lensed flat on the cap aligned with the fiber facet, and secondary reflector if one is desired, for the control of the laser energy output. A secondary reflector may also be used, as when the output angle is less than about one hundred degrees or so. A lens formed on the cap flat may be convex, or cylindrical, depending upon the output shape desired.
It has been found that the apparatus of the present invention has an efficiency, as defined by the percent of injected power exiting through the desired solid angle, of greater than ninety nine percent, as compared to between about seventy and eighty five percent of the prior art.